By its nature, a subcontractor has a contract with the Prime contractor and not the government. As such the Prime contractor should receive the unilateral determination from the cognizant PCO or ACO on that contract. There is no privity of contract  between the government and the subcontractor. The audit should have been done on the prime contractor's contract with the government.  For further clarification contact your local DCAA representative, the cognizant PCO/ACO and your servicing legal representative.